Method of making granular, light building substances



COATING R PLASTlC g 8 6 Patented Feb. 15, 1944 OFFICE METHOD OF MAKING GRANULAB, LIGHT BUILDING SUBSTANCES Carl Fabritz, Konigsberg, Preussen, Germany; vested in the. Alien Property Custodian No Drawing. Application November 14, 1938, Se-

rial No. 240,422. 1936 1 Claim.

My invention relates to a method of making a granular, light building substance.

It is an object of my invention to provide a substance of the kind referred to which possesses particularly favorable properties for building purposes, 1. e., light weight, heat and soundinsulation, adaptability, and low cost.

To this end, I provide grains of water-absorbing material, for instance, sawdust, and coat each grain individually with a binder for instance, cement which sets in the presence of water and is impermeable to water in set condition.

It has already been proposed to manufacture light building elements by impregnating waterabsorbing substances for instance, sawdust which swell to a greater or lesser extent when moistened with a very thin liquid binder, for instance, cement grouts, so as to petrify the substances.

This old process is complicated and slow since the impregnation requires a rather long time, and the mixture must be agitated repeatedly.

My novel substance, on the other hand, re-

' quires agitation of a few minutes duration only and can be used directly, for instance, for making light-weight and insulating floors, or it can be used, with addition of some more binder, for casting, molding, or otherwise producing light building elements.

In the following description, saw dust will be described as the material for the grains to be coated, and cement, with or without send, as the binder, but it is understood that I am not limited to this but may use other water-absorbing materials and other binders, provided that they are suitable for coating the grains of waterabsorbing material.

The granular substance according to my invention is prepared as follows:

The water-absorbing material, for instance, 4 litres of soft-wood sawdust with a grain size not exceeding five millimeters, and one litre of cement, are mixed in'dry condition. To this dry mixture is added a solution of a froth-forming agent, for instance soap, in water. The weight of the soap is 1.5% of the weight of the cement, and the weight of the water in which the soap is dissolved, is 2.5 times the weight of the sawdust, Waterglass at the rate of to of the weight of the water in the solution is added, and the mixture is agitated violently for about five minutes until a thick, frothy paste is produced. By the formation of the froth, so much moisture is withdrawn from the mixture that the walls of the froth globules are not supported by the In Germany December 8,

binder but the binder is deposited on the grains of sawdust as a coat. The water glass supports, the walls of the froth globules, holding the" grains in suspension until all the moisture has evaporated, and causing rapid setting of the binder on the surfaces of the grains. As the moisture is evaporated, the froth globules gradually burst. There is no adhesion between the coated grains, and the finished substance has the structure of coarse sand. It is stored in thin layers, and used directly, or for manufacturing light building elements, as will be described.

The amount of water added must obviously be so determined that the grains are only coated, and not embedded in the binder. This is determined by the nature of the water-absorbing material, of the binder, and of the froth-forming agent. This agent may be dispensed with, if

desired.

The binder may be mixed with a filler. In the case of cement as the binder, the filler is fine, and preferably dust-like sand which is admixed to the cement preferably in dry condition. I have found that sand may be added at the maximum rate of one part of sand for one part of cement, by weight, and still a satisfactory coat on each grain is obtained which prevents subsequent access of moisture to the grain.

The percentages of the constituents of the granular substance obviously vary with the crude materials used. Thus, a higher percentage of water is required for Portland cement than for iron cement, and the same rule applies to finer sand as compared with coarser. However, the principal factor which determines the percentage of the water, is the water-absorbing capacity of the grains. Sawdust can absorb about four times its own weight in water, but the amount of water must be under 2.5 times the weight of the sawdust, unless, as in the example recited above, a froth-forming agent is present, and the rate is 2.5 times. Only about one-half of the absorbing capacity of the sawdust is consequently utilized. Similarly, in the case of powdered peat whose water absorbing capacity is about 12 times its own weight, the weight of the water should be about 6 times the weight of the peat.

I have found by experiment that definite limits for the percentage of water can be determined for all crude materials under consideration. Under all conditions, the percentage of water must not be higher than what is required for setting the coating on the grains, without producing adhesion and agglomeration.

As mentioned, light building elements can be formed from the granular substance aforesaid. This operation may be performed in a single stage, combining the coating of the grains and their binding together, or the two operations are performed in separate stages. In both cases, a certain amount of binder is added beyond that required for making the granular substance. The degree of compactness in the finished elements depends upon the percentage of water present. If such percentage is but slightly in excess of the minimum required for the formation of the granular substance, the element will be .porous. It can be cast or molded under pressure but obviously there is a limit to such pressure since the element must not be crushed as this would close its pores. If the percentage of water is much in excess of the minimum, a comthis is preferably cast.

By way of example, the single-stage process may be performed as follows for making porous elements:

pact or non-porous element is produced, and

26.2 kilogrammes of best cement are intimately mixed with 10.4 kg. of dry sand having the fineness of flour. To this dry mixture are added 15.6 kg. of dry-soft-wood sawdust, and the sawdust and the dry mixture are again mixed intimately. 24.6 kg, of water are added gradually and the mass is agitated to form a paste which can be cast, or molded under moderate pressure.

I claim:

A method of making independent grains as a substance for light building elements, comprising mixing in dry condition 4 litres of soft wood sawdust with a grain size not exceeding 5 millimeters and. one litre of cement, adding a solution of a froth-forming agent, whose amount is equal toabout 1.5% of the weight of the cement, dissolved in water whose amount is equal to about 2.5 times the weight of the sawdust and 0 to 15% water glass based on the weight of water, agitating and ultimately drying the mixture.

CARL FABRITZ. 

